X-ray penetration images for medical or industrial applications were photographed using X-ray films. Subsequently, sensors emerged which convert an image directly into an electric signal without using any X-ray films. Such sensors include, for example, image pickup devices using an X-ray image intensifier+an image pickup tube or CCD, or small-sized image pickup elements such as CCDs having a photodiode as well as a scintillator provided thereon. Furthermore, in recent years, large-sized two-dimensional X-ray sensors (X-ray flat panel sensors) have been developed using a TFT (thin film transistor) technology used for liquid crystal displays.
These X-ray sensors include a type that uses a scintillator to covert an X ray into light and then uses a photodiode to convert the light into electricity, and a type that uses a semiconductor photoelectric conversion film to convert an X ray directly into an electric signal.
In these X-ray sensors, some scintillators or semiconductor photoelectric conversion films have a hygroscopic property and may consequently have their characteristics degraded. In particular, for the semiconductor photoelectric conversion films, absorbed moisture reduces electric resistance to cause a large leakage current to flow, thereby degrading their characteristics or causing a short circuit.
CCDs are so small as to be entirely packaged easily. Further, as disclosed in Patent Nos. 03-029873 and 03-077941, a configuration provided with a protective film is known in which a moisture resistive resin that can be formed into a film by vapor deposition on a CCD is formed into a film directly on a scintilator. All the disclosures in Patent Nos. 03-029873 and 03-077941 are incorporated herein by reference in their entirety.
FIG. 5 is a partial sectional view of a CCD packaged using the above-mentioned conventional techology. As shown in the figure, the above-mentioned configuration comprises light-receiving elements 52 and a signal line 53 arranged on a substrate 51, a passivation film 55 that protects the light-receiving elements 52 and the signal line 53, a scintillator 57 provided on the passivation film 55 so as to correspond to the top of the light-receiving elements 52, a protective film 511 formed so as to cover the scintillator 57 and the passivation film 55, and a sealing resin 512 provided at an end of the protective film 511 corresponding to the junction between the passivation film 55 and the protective film 511. Further, at an end of the CCD, a bonding pad 54 is provided on a main surface of the substrate 51 to connect the signal line 53 to an external portion. Furthermore, the protective film 511 has a three-layered structure including a non-moisture-permeable metal layer 59 an resin layers 510 and 58 that sandwich the metal layer 59 therebetween.
However, with this configuration, the protective film 511 is formed by plasma CVD, so that after all the films of entire CCD, including the back and side surfaces of the substrate 1, have been formed, films must be removed which have been formed on the back surface of the substrate 1 and on the bonding pad 54 in a peripheral portion of the passivation film 55. As a result, the process of producing the CCD has difficulties.
Further, with the above described technology, the protective film 511, formed by plasma CVD, is in tight contact with the scintillator 57. Accordingly, if external pressure is exerted on the protective film, it is reached to the scintillator 57 through the protective film to affect the physical resistance of the X-ray conversion film.
Furthermore, at the junction between the substrate and the protective film, the main surface of the substrate 51 is joined to the resin layers 510 and 58 of the protective film 511, with the junction sealed with the sealing resin 512, as shown in FIG. 5. However, the sealing resin 512 is jointed to the resin layers 510 and 58 of the protective film 511, and moisture may invade the scintillator 57 through this junction. Consequently, this structure does not have sufficient moisture resistance. Another problem is that a large amount of time and labor is required to produce the protective film 511 of the layered structure.
On the other hand, for large-sized x-ray sensors using the TFT technology, the method of packaging the entire substrate has the disadvantages of an operation process, insufficient airtightness, and the like. Further, the maintenance or the like of these X-ray sensors is very cumbersome. Accordingly, the method of packaging the entire substrate is not appropriate for the large-sized X-ray sensor using the TFT technology.
Another problem is that both the CCD and the large-sized X-ray sensor using the TFT technology require separate material for covering, thus increasing costs.